Cellular microvesicle pathways can be targeted to transfer genetic information between non-immune cells

The potential theragnostic (diagnostic+therapeutic) application of exosomes in diverse biomedical fields

Exosomes are membranous vesicles of 30-150 nm in diameter that are derived from the exocytosis of the intraluminal vesicles of many cell types including immune cells, stem cells, cardiovascular cells and tumor cells. Exosomes participate in intercellular communication by delivering their contents to recipient cells, with or without direct contact between cells, and thereby influence physiological and pathological processes. They are present in various body fluids and contain proteins, nucleic acids, lipids, and microRNAs that can be transported to surrounding cells. Theragnosis is a concept in next-generation medicine that simultaneously combines accurate diagnostics with therapeutic effects. Molecular components in exosomes have been found to be related to certain diseases and treatment responses, indicating that they may have applications in diagnosis via molecular imaging and biomarker detection. In addition, recent studies have reported that exosomes have immunotherapeutic applications or can act as a drug delivery system for targeted therapies with drugs and biomolecules. In this review, we describe the formation, structure, and physiological roles of exosomes. We also discuss their roles in the pathogenesis and progression of diseases including neurodegenerative diseases, cardiovascular diseases, and cancer. The potential applications of exosomes for theragnostic purposes in various diseases are also discussed. This review summarizes the current knowledge about the physiological and pathological roles of exosomes as well as their diagnostic and therapeutic uses, including emerging exosome-based therapies that could not be applied until now.

A flow cytometry assay to quantify intercellular exchange of membrane components

Membrane-compound exchange is vital for cell-to-cell communication, yet quantification of this process is difficult. Here we present a method using flow cytometry in combination with bioorthogonal and fluorescent labelling techniques to quantify the amount of exchange of cholesterol and sialylated compounds between cells. We demonstrate that direct cell-cell contact is the likely mechanism of sterol-exchange and show that by manipulating the contact time between cells using complementary coiled-coil peptides results in an enhanced exchange rate of membrane components between cells.

Exosomal trafficking in Xenopus development

Exosomes are small extracellular vesicles (EVs) secreted by many cell types in both normal and pathogenic circumstances. Because EVs, particularly exosomes, are known to transfer biologically active proteins, RNAs and lipids between cells, they have recently become the focus of intense interest as potential mediators of cell-cell communication, particularly in long-range and juxtacrine signaling events associated with adaptive immune function and progression of cancer. Among the EVs, exosomes appear particularly adapted for long-range delivery of cargoes between cells. Because of their association with disease states, the exciting potential for exosomes to serve as diagnostic biomarkers and as target-specific biomolecule delivery vehicles has stimulated a broad range of biomedical investigations to learn how exosomes are generated, what their cargoes are, and how they might be tailored for uptake by remote targets. Addressing these questions requires experimental models in which biochemically useful amounts of material can be harvested, gene expression easily manipulated, and interpretable biological assays developed. The early Xenopus embryo fulfills these model-system ideals in an in vivo context: during morphogenesis the embryo develops several large, fluid-filled extracellular compartments across which numerous tissue-specifying signals must cross, and which are abundantly endowed with exosomes and other EVs. Importantly, certain surface-facing tissues avidly ingest EVs during gastrulation. Recent work has demonstrated that EVs can be isolated from these interstitial spaces in amounts suitable for proteomic and transcriptomic analysis. With its large numbers, great cell size, well-understood fate map, and tolerance of a variety of experimental approaches, the Xenopus embryo provides a unique opportunity to both understand and manipulate the basic cell biology of exosomal trafficking in the context of an intact organism.

Serum Exosome MicroRNA as a Minimally-Invasive Early Biomarker of AML

Relapse remains the major cause of mortality for patients with Acute Myeloid Leukemia (AML). Improved tracking of minimal residual disease (MRD) holds the promise of timely treatment adjustments to preempt relapse. Current surveillance techniques detect circulating blasts that coincide with advanced disease and poorly reflect MRD during early relapse. Here, we investigate exosomes as a minimally invasive platform for a microRNA (miRNA) biomarker. We identify a set of miRNA enriched in AML exosomes and track levels of circulating exosome miRNA that distinguish leukemic xenografts from both non-engrafted and human CD34+ controls. We develop biostatistical models that reveal circulating exosomal miRNA at low marrow tumor burden and before circulating blasts can be detected. Remarkably, both leukemic blasts and marrow stroma contribute to serum exosome miRNA. We propose development of serum exosome miRNA as a platform for a novel, sensitive compartment biomarker for prospective tracking and early detection of AML recurrence.

Ectosomes and exosomes: shedding the confusion between extracellular vesicles

Long- and short-distance communication can take multiple forms. Among them are exosomes and ectosomes, extracellular vesicles (EVs) released from the cell to deliver signals to target cells. While most of our understanding of how these vesicles are assembled and work comes from mechanistic studies performed on exosomes, recent studies have begun to shift their focus to ectosomes. Unlike exosomes, which are released on the exocytosis of multivesicular bodies (MVBs), ectosomes are ubiquitous vesicles assembled at and released from the plasma membrane. Here we review the similarities and differences between these two classes of vesicle, suggesting that, despite their considerable differences, the functions of ectosomes may be largely analogous to those of exosomes. Both vesicles appear to be promising targets in the diagnosis and therapy of diseases, especially cancer.

Identification of differentially expressed genes regulated by transcription factors in glioblastomas by bioinformatics analysis

The present study aimed to identify differentially expressed genes (DEGs) regulated by transcription factors (TFs) in glioblastoma, by conducting a bioinformatics analysis. The results of the present study may provide potential therapeutic targets that are involved in the development of glioblastoma. The GSE4290 raw data set was downloaded from the Gene Expression Omnibus database, and consisted of 23 non‑tumor samples and 77 glioblastoma (grade 4) tumor samples. Robust Multichip Averaging was used to identify DEGs between the glioblastoma and non‑tumor samples. Functional enrichment analysis of the DEGs was also performed. Based on the TRANSFAC® database, TFs associated with the glioblastoma gene expression profile were used to construct a regulatory network. Furthermore, trimmed subnets were identified according to calculated Z‑scores. A total of 676 DEGs were identified, of which 190 were upregulated and 496 were downregulated. Gene Ontology analysis demonstrated that the majority of these DEGs were functionally enriched in synaptic transmission, regulation of vesicle‑mediated transport and ion‑gated channel activity. In addition, the enriched Kyoto Encyclopedia of Genes and Genomes pathway included neuroactive ligand‑receptor interaction, calcium signaling pathway, p53 signaling pathway and cell cycle. Based on the TRANSFAC® database, transcriptional regulatory networks with 2,246 nodes and 4,515 regulatory pairs were constructed. According to the Z‑scores, the following candidate TFs were identified: TP53, SP1, JUN, STAT3 and SPI1; alongside their downstream DEGs. TP53 was the only differentially expressed TF. These candidate TFs and their downstream DEGs may have important roles in the progression of glioblastoma, and could be potential biomarkers for clinical treatment.

Extracellular vesicles shed from gefitinib-resistant nonsmall cell lung cancer regulate the tumor microenvironment

Epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs), including gefitinib, are the first-line treatment of choice for nonsmall cell lung cancer patients who harbor activating EGFR mutations, however, acquired resistance to EGFR-TKIs is inevitable. The main objective of this study was to identify informative protein signatures of extracellular vesicles (EV) derived from gefitinib-resistant nonsmall cell lung cancer cells using proteomics analysis. Nano-LC-MS/MS analysis identified with high confidence (false discovery rate < 0.05, fold change ≥2) 664 EV proteins enriched in PC9R cells, which are resistant to gefitinib due to EGFR T790M mutation. Computational analyses suggested components of several signal transduction mechanisms including the AKT (also PKB, protein kinase B)/mTOR (mechanistic target of rapamycin) pathway are overrepresented in EV from PC9R cells. Treatment of recipient cells with EV harvested from PC9R cells increased phosphorylation of signaling molecules, and enhanced proliferation, invasion, and drug resistance to gefitinib-induced apoptosis. Dose- and time-dependent pharmaceutical inhibition of AKT/mTOR pathway overcame drug resistance of PC9R cells and those of H1975 exhibiting EGFR T790M mutation. Our findings provide new insight into an oncogenic EV protein signature regulating tumor microenvironment, and will aid in the development of novel diagnostic strategies for prediction and assessment of gefitinib resistance.

Cell-cell transmission of VSV-G pseudotyped lentivector particles

Many replicating viruses, including HIV-1 and HTLV-1, are efficiently transmitted from the cell surface of actively infected cells upon contact with bystander cells. In a previous study, we reported the prolonged cell surface retention of VSV-G replication-deficient pseudotyped lentivector prior to endocytic entry. However, the competing kinetics of cell surface versus dissociation, neutralization or direct transfer to other cells have received comparatively little attention. Here we demonstrate that the relative efficiency of cell-cell surface transmission can outpace "cell-free" transduction at limiting vector input. This coincides with the prolonged half-life of cell bound vector but occurs, unlike HTLV-1, without evidence for particle aggregation. These studies suggest that cell-surface attachment stabilizes particles and alters neutralization kinetics. Our experiments provide novel insight into the underexplored cell-cell transmission of pseudotyped particles.

Intra-hematopoietic cell fusion as a source of somatic variation in the hematopoietic system

Cell fusion plays a well-recognized, physiological role during development. Bone-marrow-derived hematopoietic cells have been shown to fuse with non-hematopoietic cells in a wide variety of tissues. Some organs appear to resolve the changes in ploidy status, generating functional and mitotically-competent events. However, cell fusion exclusively involving hematopoietic cells has not been reported. Indeed, genomic copy number variation in highly replicative hematopoietic cells is widely considered a hallmark of malignant transformation. Here we show that cell fusion occurs between cells of the hematopoietic system under injury as well as non-injury conditions. Experiments reveal the acquisition of genetic markers in fusion products, their tractable maintenance during hematopoietic differentiation and long-term persistence after serial transplantation. Fusion events were identified in clonogenic progenitors as well as differentiated myeloid and lymphoid cells. These observations provide a new experimental model for the study of non-pathogenic somatic diversity in the hematopoietic system.

Pseudotype-independent nonspecific uptake of gammaretroviral and lentiviral particles in human cells

The effective entry of retroviruses into target cells depends on the presence of viral envelope (Env) proteins and cognate cellular receptors, such as the murine cationic amino acid transporter-1 (mCAT-1) for the ecotropic murine leukemia virus (MLV-E). Here, we examined whether human cells internalize MLV-E or other retroviral pseudotypes irrespective of the presence of a specific receptor. Using fluorescently tagged Gag to monitor viral internalization, and treating cells with chloroquine or bafilomycin A1, we show that endocytosis is the main pathway for productive transduction with ecotropic particles, but endocytosis of retroviral particles itself does not depend on a suitable receptor or Env. Nonspecific endosomal uptake and lysosomal degradation occurred with all "illegitimate" envelope-receptor combinations tested: MLV particles pseudotyped with the ecotropic envelope or measles virus H and F proteins as well as "ecotropic" or "bald" HIV-1 particles. Kinetic studies in cell lines and primary human T lymphocytes showed the persistence of Gag-GFP signals for more than 10 days after exposure to retroviral vector particles, even in the absence of a suitable receptor. Further studies testing the Gag-mediated transfer of protein or retroviral mRNA revealed that nonspecific endocytosis prevented the release of functional particle-associated proteins and nucleic acids into the cytosol. We conclude that receptor-targeted retroviral particles are unlikely to escape nonspecific cellular uptake unless appropriate protective principles are discovered. Conversely, as lysosomal degradation was found to inactivate mRNA and proteins embedded into retroviral particles, receptor targeting is a useful strategy for both transient and permanent cell modification by retrovirus-like particles.

Genetically engineered mesenchymal stem cells as a proposed therapeutic for Huntington's disease

There is much interest in the use of mesenchymal stem cells/marrow stromal cells (MSC) to treat neurodegenerative disorders, in particular those that are fatal and difficult to treat, such as Huntington's disease. MSC present a promising tool for cell therapy and are currently being tested in FDA-approved phase I-III clinical trials for many disorders. In preclinical studies of neurodegenerative disorders, MSC have demonstrated efficacy, when used as delivery vehicles for neural growth factors. A number of investigators have examined the potential benefits of innate MSC-secreted trophic support and augmented growth factors to support injured neurons. These include overexpression of brain-derived neurotrophic factor and glial-derived neurotrophic factor, using genetically engineered MSC as a vehicle to deliver the cytokines directly into the microenvironment. Proposed regenerative approaches to neurological diseases using MSC include cell therapies in which cells are delivered via intracerebral or intrathecal injection. Upon transplantation, MSC in the brain promote endogenous neuronal growth, encourage synaptic connection from damaged neurons, decrease apoptosis, reduce levels of free radicals, and regulate inflammation. These abilities are primarily modulated through paracrine actions. Clinical trials for MSC injection into the central nervous system to treat amyotrophic lateral sclerosis, traumatic brain injury, and stroke are currently ongoing. The current data in support of applying MSC-based cellular therapies to the treatment of Huntington's disease is discussed.

Examination of mesenchymal stem cell-mediated RNAi transfer to Huntington's disease affected neuronal cells for reduction of huntingtin

Huntington's disease (HD) is a fatal, autosomal dominant neurodegenerative disorder caused by an expanded trinucleotide (CAG) repeat in exon 1 of the huntingtin gene (Htt). This expansion creates a toxic polyglutamine tract in the huntingtin protein (HTT). Currently, there is no treatment for either the progression or prevention of the disease. RNA interference (RNAi) technology has shown promise in transgenic mouse models of HD by reducing expression of mutant HTT and slowing disease progression. The advancement of RNAi therapies to human clinical trials is hampered by problems delivering RNAi to affected neurons in a robust and sustainable manner. Mesenchymal stem cells (MSC) have demonstrated a strong safety profile in both completed and numerous ongoing clinical trials. MSC exhibit a number of innate therapeutic effects, such as immune system modulation, homing to injury, and cytokine release into damaged microenvironments. The ability of MSC to transfer larger molecules and even organelles suggested their potential usefulness as delivery vehicles for therapeutic RNA inhibition. In a series of model systems we have found evidence that MSC can transfer RNAi targeting both reporter genes and mutant huntingtin in neural cell lines. MSC expressing shRNA antisense to GFP were found to decrease expression of GFP in SH-SY5Y cells after co-culture when assayed by flow cytometry. Additionally MSC expressing shRNA antisense to HTT were able to decrease levels of mutant HTT expressed in both U87 and SH-SY5Y target cells when assayed by Western blot and densitometry. These results are encouraging for expanding the therapeutic abilities of both RNAi and MSC for future treatments of Huntington's disease.

Exosomes/microvesicles: mediators of cancer-associated immunosuppressive microenvironments

Cancer cells, both in vivo and in vitro, have been demonstrated to release membranous structures, defined as microvesicles or exosomes, consisting of an array of macromolecules derived from the originating cells, including proteins, lipids, and nucleic acids. While only recently have the roles of these vesicular components in intercellular communication become elucidated, significant evidence has demonstrated that tumor exosomes can exert a broad array of detrimental effects on the immune system-ranging from apoptosis of activated cytotoxic T cells to impairment of monocyte differentiation into dendritic cells, to induction of myeloid-suppressive cells and T regulatory cells. Immunosuppressive exosomes of tumor origin can be found within neoplastic lesions and in biologic fluids from cancer patients, implying a potential role of these pathways in in vivo tumor progression and systemic paraneoplastic syndromes. Through the expression of molecules involved in angiogenesis promotion, stromal remodeling, signaling pathway activation through growth factor/receptor transfer, chemoresistance, and genetic intercellular exchange, tumor exosomes could represent a central mediator of the tumor microenvironment. By understanding the nature of these tumor-derived exosomes/microvesicles and their roles in mediating cancer progression and modulating the host immune response will significantly impact therapeutic approaches targeting exosomes.